Light regulation of pigment and photosystem biosynthesis in cyanobacteria

• Cyanobacterial phytochromes and cyanobacteriochromes are highly diverse.
• These photosensors are modular and integrate multiple light wavelength signals.
• Coupling photosensory domains to multiple output domains allows diverse responses.
• Far-red light causes extensive remodeling of PSI, PSII and phycobilisomes.
• Multiple photoreceptors finely regulate complementary chromatic acclimation.

Most cyanobacteria are obligate oxygenic photoautotrophs, and thus their growth and survival is highly dependent on effective utilization of incident light. Cyanobacteria have evolved a diverse set of phytochromes and cyanobacteriochromes (CBCRs) that allow cells to respond to light in the range from ∼300 nm to ∼750 nm. Together with associated response regulators, these photosensory proteins control many aspects of cyanobacterial physiology and metabolism. These include far-red light photoacclimation (FaRLiP), complementary chromatic acclimation (CCA), low-light photoacclimation (LoLiP), photosystem content and stoichiometry (long-term adaptation), short-term acclimation (state transitions), circadian rhythm, phototaxis, photomorphogenesis/development, and cellular aggregation. This minireview highlights some discoveries concerning phytochromes and CBCRs as well as two acclimation processes that improve light harvesting and energy conversion under specific irradiance conditions: FaRLiP and CCA.

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